Recently, a technique concerning the use of MOS (Metal Oxide Semiconductor) technology applied to a microcomputer has progressed remarkably, and integrated circuits are being produced with a high integration ratio so that a microcomputer having a high performance and high function is now actuating available. There has been introduced a processor for such a microcomputer as described, for instance, in the second to 4th paragraphs on page 55 of "Microprocessors" in IEEE Spectrum, published in Jan., 1985. The prior art discloses that the central processing unit for processing an operand corresponding to an instruction and a memory unit for storing the operand are mounted on the same chip. By providing a microprocessor and a memory on the same chip, the signal delay of a signal line connecting the microprocessor and the memory can be reduced significantly. And further, by providing the microprocessor and the memory on the same chip, when the microprocessor accesses the memory for fetching a program or processing an operand, the transmission timing, the access time of the control signal or the data which is received and transmitted between the memory and the microprocessor is reduced. By enlarging the data bus width or forming the memory and the microprocessor on the same chip, the processing power as a whole is improved.
However, when the width of the data bus is increased, the number of terminals necessary for connecting the microprocessor and an external memory located outside the chip is increased for receiving and sending the data therebetween. As a result, there is a drawback that the number of pins of the package, in which the microprocessor is enclosed, is increased. In the prior microcomputer equipped with a memory on the same chip, since the first control configuration (which is the timing of the control signal or the timing of receiving and sending data) for accessing the memory within the chip by use of the microprocessor and the second control configuration for accessing an external memory located outside the chip by use of the microprocessor are not processed of the operand especially considering both control configurations, there is a drawback in that the first width of the data bus connecting the processor and the memory within the same chip has to be equal to the second width of the data bus connecting the processor and the external memory located outside the chip.